Plasma urea nitrogen concentration and growth performance of finishing pigs fed sorghum-soybean meal, low-protein diets

To determine the lowest CP level in sorghum-soybean meal diets of finishing pigs using plasma urea nitrogen (PUN) concentration as rapid response criterion, two experiments were conducted. In experiment 1, four CP (%) levels: T1) 14.0, control; T2) 12.5; T3) 11.0; and T4) 9.5, were tested in a crossover design with four periods of 7 days each. On the last day of each period, blood was collected to determine PUN. The lowest PUN indicated that CP can be reduced up to 9.5%. The best regression model (highest R² and lowest SEM) was the nonlinear exponential. In experiment 2, three CP (%) levels were: T1) 14; T2) 12.5; and T3) 9.5. The feed: gain ratio increased and the longissimus muscle area and PUN were reduced as CP was reduced. These results indicate that PUN can be reduced with lower dietary CP.